Finding digital signals

Is there a really easy to use method to see if there is some type of digital communications being passed through a wire? I am looking for something I can hand to another person with 2 minutes of instruction that will give them about a 90% chance they will identify a wire that has SPI, I2C, UART, maybe USB or UART data going on. There is no need to figure out anything other than "there is something going on in this wire." An Oscope is normally the method but that is too complicated for my application. I am wondering if a tone probe might work. Any ideas? Thanks.

Re: Finding digital signals

The easiest way to identify signal activity on a line is the digital logic probe that sounds a beeper when it identifies a logic low. So, some train of beeps present on probing the line will indicate signalling activity.